1. Field of Invention
The present invention relates to a laser technology, and more particularly to a device for single-shot pulse contrast measurement.
2. Description of Related Arts
Temporal contrast (i.e. signal to noise ratio) of the laser pulse is one major challenge of the intense femtosecond chirped pulse amplifier. It not only requires designing more precise laser systems and pulse cleaning technology, but also challenges the technology of measuring the pulse contrast. The pulse contrast measurement mainly depends on the nonlinear correlation technology, i.e. retrieving a pulse contrast curve of an under-test pulse through realizing a cross-correlation of sum frequency generation (SFG) or difference frequency generation (DFG) between a clean sampling pulse and the under-test pulse in a nonlinear crystal and measuring the dependence of the SFG signal (or the idler) on the time delay. The clean sampling pulses are basically produced by the second harmonic generation (SHG) of the under-test pulse. At present, the time-scanning measurement has a dynamic range of 1011 and has been commercialized into products. However, most intense CPA (chirped pulse amplification) systems have a low pulse repetition rate or even no pulse repetition rate, so the technology of measuring pulse contrast in the single-shot must be developed. The system for measuring the pulse contrast usually reaches a certain temporal window through the time-to-space encoding. Recently the temporal window and the dynamic range of the single-shot measurement have respectively reached 200 ps and 109.
What is extremely important for the single-shot pulse contrast measurement is the capability to precisely illustrate the pulse background and the fine structure possibly existing therein. This not only necessitates a high dynamic range and temporal resolution, but also requires a high-fidelity contrast measurement. With time-to-space encoding and the image relay from the correlating crystal to the multi-element detector, the fidelity issue of single-shot measurement of will be more complex than that of time-scanning measurement. In single-shot cross-correlator, two factors in forms of scattering noise and artificial spikes may easily degrade the measurement fidelity. The scattering noise can submerge the real background and tiny structure of the measured trace. While the artifacts, mainly caused by multi-reflection in essence, can be confused with or cover the real structures. Both of the two factors result in an uncorrected measurement.